1. Field of the Invention
This invention relates to a variable speed gear wherein a shift shaft and a shift fork are moved in an axial direction in response to a shift movement of a shift operation member to move a clutch member on a power transmission shaft and to select a shift position.
2. Description of Background Art
Various types of variable speed gears for use with a gear type variable speed mechanism which includes a plurality of gear trains are conventionally known for selecting one of the gear trains. As a speed change mechanism for use with a variable speed gear of the type described, for example, a speed change mechanism of the selective sliding type is provided wherein a power transmission gear is moved on a power transmission shaft to select meshing of the gear. In addition, another speed change mechanism of the normally meshing type is provided wherein a power transmission gear is normally held in a meshing state and control for engagement and disengagement of the power transmission gear is performed. A power transmission shaft is provided on which the power transmission gear is supported for rotation. The above device is well known and conventionally. It is to be noted that also it is well known to use a synchromesh mechanism (synchronous mesh mechanism) for the normally meshing type speed change mechanism.
A transmission which uses such a variable speed gear as described above is popularly adopted as transmissions for two-wheeled vehicles, four-wheeled vehicles and so forth. A variable speed gear disclosed in Japanese Patent No. 3325843 is consider as an example of a transmission of this type. This variable speed gear includes a clutch member disposed for movement in an axial direction on a power transmission shaft with a shift fork having an end held in engagement with the clutch member. A shift drum is provided on which the shift fork is attached with a cam mechanism provided between the shift drum and the shift fork. The shift drum is rotated in response to a shift operation to move the shift fork in the axial direction through the cam mechanism to move the clutch member in the axial direction on the power transmission shaft thereby to select a shift position.
A variable speed gear is usually configured such that, when a selection of a shift position (that is, a speed changing operation) is performed, the shift position is detected and control corresponding to the shift position is performed. Therefore, the apparatus disclosed in Japanese Patent No. 3325843 mentioned hereinabove detects a rotational angular position of the shift drum to detect the shift position.
In addition, not only is a variable speed gear of the type which uses a shift drum as described above available but also another variable speed gear is available which is configured such that a shift fork is coupled and attached to a shift shaft disposed to extend in parallel to a power transmission shaft such that the shift shaft and the shift fork are moved in an axial direction in response to a shift operation to move a clutch member in the axial direction on the power transmission shaft to select a shift position. In a variable speed gear wherein a shift shaft is moved in an axial direction to perform a speed changing operation in this manner, such a shift position detection apparatus as described in Japanese Patent No. 3325843 mentioned hereinabove cannot be used. A plurality of position sensors for detecting the position of the shift shaft in the axial direction corresponding to the individual shift positions are required. Therefore, the variable speed gear encounters a problem wherein the configuration of the shift position detection apparatus is liable to have an increase in scale and be complicated.